On Windows, you should be able to set `security.enterprise_roots.enabled` to true. Might have to restart Firefox for it to recognize.

Enterprise root certs are different from client certs even if some (perhaps many or most) client certs were signed by an enterprise root. A client cert is about providing identity information/proofs (instead of or in addition to traditional credentials). I hope mozilla isn't conflating the two though I can see how they might decide that turning on one thing gets you the other as well.